Re: [alsa-devel] [PATCH 3/7] ASoC: tegra: Add tegra-pcm driver

On 01/08/11 07:36, ext Stephen Warren wrote:

This provides an ASoC platform driver that manages Tegra's APB DMA controller.

Signed-off-by: Stephen Warren swarren@nvidia.com

sound/soc/tegra/tegra_pcm.c | 401 +++++++++++++++++++++++++++++++++++++++++++ sound/soc/tegra/tegra_pcm.h | 55 ++++++ 2 files changed, 456 insertions(+), 0 deletions(-) create mode 100644 sound/soc/tegra/tegra_pcm.c create mode 100644 sound/soc/tegra/tegra_pcm.h

diff --git a/sound/soc/tegra/tegra_pcm.c b/sound/soc/tegra/tegra_pcm.c

...

•   switch (cmd) {
  

•   case SNDRV_PCM_TRIGGER_START:
  

•           prtd->dma_pos = 0;
  

•           prtd->dma_pos_end = frames_to_bytes(runtime, runtime->periods * runtime->period_size);
  

•           prtd->period_index = 0;
  

•           prtd->dma_req_idx = 0;
  

•           /* Fall-through */
  

•   case SNDRV_PCM_TRIGGER_RESUME:
  

•   case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
  

•           spin_lock_irqsave(&prtd->lock, flags);
  

•           prtd->running = 1;
  

•           spin_unlock_irqrestore(&prtd->lock, flags);
  

•           tegra_pcm_queue_dma(prtd);
  

•           tegra_pcm_queue_dma(prtd);
  

•           break;
  

•   case SNDRV_PCM_TRIGGER_STOP:
  

•   case SNDRV_PCM_TRIGGER_SUSPEND:
  

•   case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
  

•           spin_lock_irqsave(&prtd->lock, flags);
  

•           prtd->running = 0;
  

•           spin_unlock_irqrestore(&prtd->lock, flags);
  

•           tegra_dma_dequeue_req(prtd->dma_chan, &prtd->dma_req[0]);
  

•           tegra_dma_dequeue_req(prtd->dma_chan, &prtd->dma_req[1]);
  

Does tegra_dma_dequeue_req stops the ongoing DMA transaction as well? If I read the code right, you have two DMA requests placed at every given time (one is currently running, the other is waiting). What happens if the dma_req[0] was running, and you dequeue it? Will the DMA engine moves to process the dma_req[1], which will be stopped a moment later?